Why would you tip a delivery guy?
Because you CHOOSE to, or not to; because they're providing an additional service. You could certainly have picked up the furniture.
Do you tip the Fed Ex guy? UPS guy?
Rarely - but I tip the maintenance man employed by my apartment complex who accepts the UPS delivery and places it in my apartment so I don't have to go to UPS and pick it up myself because he's going out of his way for me; by the way, the year I was getting a lot of UPS shipments and at the UPS facility about every other day, I did bring the counter people a food gift to share. That I got to the head of the lonnnnnnnnnnnnnnng line was COMPLETE coincidence - I was the only person in that line who'd called ahead of time, so my package was waiting for me 
Does the restaurant tip the guy when he delivers their linens?
Regular weekly delivery? Probably not.
Does the bakery tip the guy who delivers the stove?
One time/rare delivery of heavy restaurant equipment that may need to be correctly placed and installed? I wouldn't doubt it.
Does the grocery store tip the guy who delivers
What "guy" who delivers what? Merchandise to the store to sell? Not likely - see 'linens', above. Actual grocery delivery, from the store to a customer? Uh, the customer would tip - yes, despite a delivery charge - THAT goes to the store.I especially do not understand when you have already paid the fee for delivery? It is not as if these guys are getting paid $3 an hour.
The next thing I am going to hear is you need to tip the janitor at work for changing out your garbage can!